There has been used a technique for comparing (i) input image data obtained by reading a document image with a scanner and (ii) a (reference image (pre-registered image), so as to determine similarity between the input image data and the reference image, and preventing a process (such as copy etc.) for the input image data in case where the input image data is determined as being similar to the reference image.
Examples of a method for determining similarity include: a method in which a keyword is extracted from an image with OCR (Optical Character Reader) so as to carry out matching with the keyword; a method in which a target image is limited to an image with ruled lines and matching is carried out based on features of the ruled lines; and a method in which similarity is determined based on distribution of color components of input image data and a reference image.
Furthermore, Patent Document 1 (Japanese Unexamined Patent Publication: Tokukaihei 7-282088 (published on Oct. 27, 1995) discloses a technique in which a descriptor that is invariable to distortion caused by digitalization of an input document or to a difference between the input document and a document database is generated based on feature points of the input document, and matching between the input document and a document in the document database is performed using the descriptor and a descriptor database which stores descriptors and which indicates a list of documents including features from which descriptors are extracted. In the technique, when the descriptor database is scanned, votes for individual documents in the document database are accumulated, and a document with the largest number of votes or a document whose number of votes is over a certain threshold value is considered as a matching document.
Furthermore, an example of a technique for controlling a process for input image data in accordance with the result of similarity determination is as follows: in order to prevent forgery of a bill or securities by a color image forming apparatus, it is determined whether input image data is identical to image data such as a bill or securities (reference image) or not based on a pattern extracted from the input image data, and when the input image data is identical to the image data of the reference image, a specific pattern is given to an output image so as to specify the image forming apparatus that carries out copying, a copied image is blacked out, or copying is prevented.
However, according to the aforementioned conventional techniques, in case where the input image data is determined as being identical to image data of the reference image, processes carried out with respect to the input image data can be restricted (there are performed processes, such as addition of a specific pattern, restriction of processing by blacking out a copy image, and prohibiting of a copying operation), but a process for the input image data is set to a certain process (addition of a specific pattern, restriction of processing by blacking out a copy image, and prohibiting of a copying operation) in accordance with whether the input image data is similar to image data of the reference image. This raises such problem that the image can be less freely processed and it is troublesome to use functions thereof.
For example, in offices of recent companies and the like, it is often that there are provided multi-function printers each having a copying function, a facsimile function, a filing function, an electronic distribution function, and the like. Further, it is often that each of these multi-function printers is shared by a plurality of users or a plurality of groups. In such cases, it is often required to carry out a process (copying, facsimile transmission, filing, electronic distribution, and the like) with respect to a document (input image data) in accordance with a predetermined rule having been determined for each user or each group. Further, it may be required to carry out a predetermined process with respect to the document in accordance with a type of the document or a similar condition.
However, the conventional technique takes into consideration only such arrangement that the process for the document is prohibited or restricted in case where it is determined that the document is similar to the reference image. As a result, what process should be carried out cannot be set in accordance with a user, a group of the user, a type of the document, and the like, and the matching result. Thus, what process should be carried out has to be set by the user in detail every time a process such as copying, facsimile transmission, filing, electronic distribution, or the like with respect to the document is carried out. This is so troublesome.